Search

Objective: To determine whether muscarinic receptor antagonism affects stretching-induced release of ATP., Materials and Methods: Mucosal strips, dissected from guinea pig (male, 450g; n = 10) urinary bladders, were placed in horizontal organ baths and superfused with Ca(2+) -free Tyrode's solution. Superfusate samples were taken pre- and post- intervention (rapid stretching or relaxation) and ATP concentration was quantified using a luciferin-luciferase assay. The effect of muscarinic acetylcholine receptor antagonism on ATP release was assessed by addition of methoctramine (1 µM) and 4-DAMP (10 nM)., Results: Rapid stretching (0 to 13.3 ± 1.2 mN; no. strips = 20) increased ATP in the superfusate to a median threefold increase over basal levels. After a period of equilibration, tension in the mucosal strips relaxed until it had reached a new steady-state after 60 min and stretching was repeated. In the presence of 4-DAMP (10 nM) or methoctramine (1 µM), ATP concentrations after stretching reduced to 61% or 20%, respectively. By contrast, ATP concentrations in mucosa-matched controls, perfused with vehicle, increased in response to stretching by 391% and 1500%, respectively. Rapid relaxation also stimulated ATP release. This release did not appear to be sensitive to 4-DAMP or methoctramine., Conclusions: An alteration of resting mucosal tension is the key determinant of ATP release, as ATP is released from the mucosa in response to both stretching and relaxation. Muscarinic receptor antagonism inhibits stretching-evoked ATP release from bladder mucosa, suggesting that anticholinergic agents used to treat human lower urinary tract pathologies act on urothelial muscarinic receptors., (© 2012 BJU INTERNATIONAL.)

Extracellular ATP has been previously shown to activate calcium signalling in pituitary cell populations [1] but the particular cell types involved have not been identified. We used video imaging of Fura-2 loaded into single rat pituitary cells and identified as lactotrophs to study the effects of extracellular ATP on [Ca2+]i. ATP does not permeabilize the cells as shown by exclusion of propidium iodide. ATP causes two types of calcium transients in lactotrophs. The most common response is a rapid increase in [Ca2+]i that decays slowly and is terminated by washout of ATP. This type of response is also seen in calcium-free medium, demonstrating mobilization of calcium stores dependent upon the presence of the agonist. ATP also stimulates calcium entry as detected by Mn(2+)-quenching of Fura-2. ATP in Mg(2+)-free medium and ATP gamma S are effective agonists suggesting ATP4- is the active form. The presence of P2-purinoceptors is apparent because ATP, ADP and AMP increase [Ca2+]i in decreasing order of potency and adenosine has no effect. ATP-induced calcium transients are reduced by the P2-purinoceptor antagonists suramin and quinidine. UTP is equipotent with ATP and defines the receptor subtype as P2U. We conclude that ATP4- acts on rat lactotrophs via P2U-purinoceptors to elevate [Ca2+]i from intracellular and extracellular sources.